Conventionally, tennis balls are manufactured with the use of a textile having a felted surface. This means that the outer surface of the ball presents a layer of entangled fibres. The felt has a significant influence on the flight characteristics and feel of a tennis ball. Over the last 50 years a large number of attempts have been made to propose other types, (generally cheaper or having an increased resistance to wear) of non-felted tennis ball covering but they have been found unsuccessful to equal the feel and characteristic of the felted fabric and to replace the classic felted covering.
Thus, U.S. Pat. No. 4,874,169 describes a game ball having various types of depressions on one of its hemisphere. One particular ball is a tennis ball (see FIG. 5) having one hemisphere covered with a standard tennis ball covering and another covered by a plastic-like smooth material having grooves radiating from its pole.
It has been further proposed in U.S. Pat. No. 1,287,766 to replace the standard fabric covering of the tennis ball by a smooth and soft rubber-like material. Said rubber covering is provided with regular holes in order to mimic the skin friction of a standard tennis ball felt cover.
U.S. Pat. No. 4,616,828 describes a tennis ball having a deep groove extending in the rubber spherical core of the ball in order to control the air turbulence during the ball trajectory. In one embodiment it is proposed to cover the ball with a non-felted fabric made of woven synthetic filaments or fibres. These synthetic filaments are woven so as define a series of rectangular areas.
In U.S. Pat. No. 1,376,778 it is proposed to protect the seam of the textile and to produce a better controlling effect by compressing the outer fabric once provided on a tennis ball at various points along the seam. However, applying pressure to the tennis ball is not recommended as the pressure may alter the internal shape of the core of the ball. Also, compressed area obtained by such compression method are not very wear-resistant and disappear rapidly when used on a tennis ball.
A problem with the modern game of tennis is that as players become more and more powerful, less skill is needed to play the game. The game is fast and rarely are more than two or three shots played in a rally. This makes the games less enjoyable for spectators.
It would be desirable to have a felted tennis ball covering which would allow for greater control over the flight of the tennis ball. More particularly it would be desirable to have a felted tennis covering which, when applied to a tennis ball, alters substantially the flight and/or rebound characteristics when spin is imparted by the player to the ball. This would allow tennis players by imparting spin to various degrees to cause the ball to vary its course to a differing extent as it flies through the air and also to achieve a greater deviation from the expected path of the ball's rebound from the court.